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Steamhead
2nd Mar 2011, 19:38
I understand that engine surge can be caused by the tip clearances getting larger because of wear. Is it policy for some airlines to leave the engine on the wing until they surge? and then send them for overhaul. I believe that FADC can help to control surge but has its limits. I am not a turbine engineer but a 5/8 fitter.

grounded27
2nd Mar 2011, 21:52
A jet engine stays on wing until it meets a pre-designed overhaul time limit or sustains damage beyond pre set tolerance. Most modern get engines do not surge and when they do it is reason for removal, most non fadec engines can stay on wing after a surge. It is common to hear old straight pipe engines stall, often in reverse thrust.

lomapaseo
3rd Mar 2011, 01:26
General answers for a general question.

Policy is in the eye of the beholder

The bean counters with proper software can track an engine's performance and remove it just-in-time to save the most money between fuel burn costs, repair costs and out-of-service time.

Since a single surge is not considered a safety detriment, it may be used as a point of information according to the intent of the lowest cost management plan. (note that different requirements for different engines play a roll)

Things that do attract the greater attention are shutdowns, air-turn-backs, diversions and forced removals

Now FADECs are good but they aren't good enough to prevent a surge if you wear out an engine.

And those old nasties that surge in reverse are wearing out engines pretty fast by letting them surge in reverse. (the question there is how many times?)

barit1
3rd Mar 2011, 03:46
Most common cause for removal is probably EGT (ITT) margin deterioration - not making rated thrust within the redline.

But excess fuel burn can also drive an engine off wing, especially when fuel is $$$mucho. Excessive tip clearance is usually associated with both of the above.

But there are other causes - FOD, LCF cyclic limits, bearing/lube contamination, casing cracks, AD compliance, ....

spannersatcx
3rd Mar 2011, 08:20
A lot of modern engines DO surge and when they do it is NOT always a reason to remove it.:ok:

grounded27
3rd Mar 2011, 12:40
A lot of modern engines DO surge and when they do it is NOT always a reason to remove it

You can hardly say that the amount of FADEC powered engine stalls is significant to the amount say stalls v/s hours in service of older engines. I personally have yet to see a FADEC engine stall, while they certianly have I just have never been in earshot (I am in earshot of easily 1000 TO's and landings a week). The JT9 and CF6-6 and -50 are pretty much the same era engine. When we stall a CF6 it comes off the wing for inspection. I have had JT9's blow fireballs at me at 85% n1 on the fence and it was never a big deal the pratt used to be a tougher engine while the GE produced better econemy.

When newer engines fail it is usually catastropic, high tolerance, low clearance, higher compression and heat. When they go bang it often results in damage. Trips me out thinking of old JT3 powered DC8's landing, I mean every damb time the applied reverse thrust there was at least one engine popping.